[unreadable] Data from our laboratory and others have demonstrated that several vitamin D compounds, including 1a,25- dihydroxyvitamin D3 [1,25(OH)2D3] and 25-hydroxyvitamin D3 (25OHD3) inhibit the proliferation of primary human prostatic epithelial cells and human prostate cancer cell lines. We have demonstrated that genistein can synergize with vitamin D to inhibit prostatic cell growth. We hypothesize that genistein and vitamin D will cooperate to inhibit prostate tumor development in a genetic model of mouse prostate cancer development. The intracellular proteins and pathways that mediate genistein and vitamin D-induced synergistic growth inhibition are not defined. We hypothesize that genistein and vitamin D synergistically inhibit prostatic cell cycle arrest via multiple mechanisms, and that at least one mechanism is by genistein-mediated increase in vitamin D receptor (VDR) levels which leads to increased sensitivity to 1,25(OH)2D3-mediated increases in the CKIs p21 and/or p27. The primary goal of Aim 1 is to test the requirements of p21 and p27 in genistein and vitamin D (25OHD3 or 1,25(OH)2D3)- mediated synergistic growth arrest of prostatic epithelial cells. Our experimental approach is to use two complimentary, yet distinct systems; cultured mouse and human prostatic epithelial cells. We will use cultured prostatic cells from mice with targeted disruption of p21, p27 or both. This system will allow us to use the experimental rigor of an absolute lack of CKI expression to assess the requirement(s) of these CKIs in the growth inhibition we observe. We will also suppress CKI mRNA expression in primary human prostatic epithelial cells using RNAi . The mechanism of regulation of CKI expression will be determined in Aim 2. Together, the experimental rigor afforded by the reverse genetics mouse studies, combined with the relevance of the studies in human cells will define the mediating roles of theses CKIs in prostatic growth inhibition by vitamin D compounds. Aim 3 will test the role of genistein-mediated VDR upregulation in the synergistic growth inhibition we observe. Aim 4 will evaluate the efficacy of combined genistein and vitamin D supplementation as a prostate cancer chemoprevention agent using a mouse genetic model of prostate tumor development. Our long-term goals are to develop a mechanistic-based chemoprevention strategy that utilizes dietary supplementation with vitamin D and soy isoflavanoid. [unreadable] [unreadable] [unreadable]